IBDKinship: An LR-based kinship analysis method for distant relatives up to the seventh degree using IBD segments

Area of Science:

• Forensic genetics
• Population genetics
• Statistical genetics

Background:

• Short tandem repeat (STR) methods are standard for close kinship analysis but lack resolution for distant relationships.
• Accurate identification of biological relationships is crucial for paternity testing, missing persons, and disaster victim identification.
• Genome-wide data offers complementary evidence for resolving distant kinship.

Purpose of the Study:

• To develop and evaluate IBDKinship, a novel likelihood ratio (LR) method for kinship inference and testing.
• To improve the resolution of kinship analysis across a wide range of relationship degrees, especially for distant relatives.
• To provide a genome-wide evidence-based framework for forensic genetic kinship analysis.

Main Methods:

• Developed IBDKinship, a likelihood ratio method modeling identity-by-descent (IBD) segment number, length, and chromosomal distribution.
• Utilized simulated pedigree data from the 1000 Genomes Project with variants from the Illumina Global Screening Array (GSA).
• Evaluated performance for relationship inference and kinship testing across first- to seventh-degree relationships.

Main Results:

• IBDKinship achieved 100% accuracy for first-degree and 99.32% for second-degree relationships.
• Accuracy for distant relationships (third to seventh degree) ranged from 46.05% to 92.99%.
• Kinship testing demonstrated 100% sensitivity and specificity up to the fourth degree, with high effectiveness for more distant relationships.

Conclusions:

• IBDKinship provides a robust likelihood-based framework for genome-wide identity-by-descent segment evidence in kinship analysis.
• The method enhances resolution for both close and distant relationships, complementing existing STR-based approaches.
• High-quality genotype data yields the strongest support, particularly for close to moderately distant relationships.